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Radio-loud Narrow Line Seyfert 1 under a different perspective: a revised black hole mass estimate from optical spectropolarimetry

Radio-loud Narrow Line Seyfert 1 under a different perspective: a revised black hole mass estimate from optical spectropolarimetry
Radio-loud Narrow Line Seyfert 1 under a different perspective: a revised black hole mass estimate from optical spectropolarimetry
Several studies indicate that radio-loud (RL) active galactic nuclei (AGNs) are produced only by the most massive black holes (BH), MBH ∼ 108–1010 M⊙. This idea has been challenged by the discovery of RL Narrow Line Seyfert 1 (RL NLSy1), having estimated masses of MBH ∼ 106–107 M⊙. However, these low MBH estimates might be due to projection effects. Spectropolarimetry allows us to test this possibility by looking at RL NLSy1s under a different perspective, i.e. from the viewing angle of the scattering material. We here report the results of a pilot study of Very Large Telescope spectropolarimetric observations of the RL NLSy1 PKS 2004−447. Its polarization properties are remarkably well reproduced by models in which the scattering occurs in an equatorial structure surrounding its broad-line region, seen close to face-on. In particular, we detect a polarized Hα line with a width of ∼9000 km s−1, ∼6 times broader than the width seen in direct light. This corresponds to a revised estimate of MBH ∼ 6 × 108 M⊙, well within the typical range of RL AGN. The double-peaked polarized broad Hα profile of the target suggests that the rare combination of the orientation effects and a broad line region dominated by the rotation might account for this class of objects, casting doubts on the virial estimates of BH mass for type-I AGN.
1745-3925
L69-L71
Baldi, Ranieri Diego
c416ed4c-5d1c-48ee-989c-3a8ab38cd124
Capetti, Alessandro
4b5a2e61-ac39-42ca-aa3e-15983b11146c
Robinson, Andrew
11e9f1f6-1445-436a-a482-7208201c83ac
Laor, Ari
c05ad4c1-3fb4-465a-ab9e-8928b410043c
Behar, Ehud
04fd38d9-e172-4ae9-a530-9418b301e041
Baldi, Ranieri Diego
c416ed4c-5d1c-48ee-989c-3a8ab38cd124
Capetti, Alessandro
4b5a2e61-ac39-42ca-aa3e-15983b11146c
Robinson, Andrew
11e9f1f6-1445-436a-a482-7208201c83ac
Laor, Ari
c05ad4c1-3fb4-465a-ab9e-8928b410043c
Behar, Ehud
04fd38d9-e172-4ae9-a530-9418b301e041

Baldi, Ranieri Diego, Capetti, Alessandro, Robinson, Andrew, Laor, Ari and Behar, Ehud (2016) Radio-loud Narrow Line Seyfert 1 under a different perspective: a revised black hole mass estimate from optical spectropolarimetry. Monthly Notices of the Royal Astronomical Society: Letters, 458 (1), L69-L71. (doi:10.1093/mnrasl/slw019).

Record type: Article

Abstract

Several studies indicate that radio-loud (RL) active galactic nuclei (AGNs) are produced only by the most massive black holes (BH), MBH ∼ 108–1010 M⊙. This idea has been challenged by the discovery of RL Narrow Line Seyfert 1 (RL NLSy1), having estimated masses of MBH ∼ 106–107 M⊙. However, these low MBH estimates might be due to projection effects. Spectropolarimetry allows us to test this possibility by looking at RL NLSy1s under a different perspective, i.e. from the viewing angle of the scattering material. We here report the results of a pilot study of Very Large Telescope spectropolarimetric observations of the RL NLSy1 PKS 2004−447. Its polarization properties are remarkably well reproduced by models in which the scattering occurs in an equatorial structure surrounding its broad-line region, seen close to face-on. In particular, we detect a polarized Hα line with a width of ∼9000 km s−1, ∼6 times broader than the width seen in direct light. This corresponds to a revised estimate of MBH ∼ 6 × 108 M⊙, well within the typical range of RL AGN. The double-peaked polarized broad Hα profile of the target suggests that the rare combination of the orientation effects and a broad line region dominated by the rotation might account for this class of objects, casting doubts on the virial estimates of BH mass for type-I AGN.

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More information

Accepted/In Press date: 4 February 2016
e-pub ahead of print date: 19 February 2016
Published date: May 2016

Identifiers

Local EPrints ID: 412602
URI: https://eprints.soton.ac.uk/id/eprint/412602
ISSN: 1745-3925
PURE UUID: bfc462a4-fa9e-45cd-8921-fecf2c0fa36b

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Date deposited: 24 Jul 2017 16:32
Last modified: 13 Mar 2019 19:39

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